Determining the material composition of a sample becomes actual in various cases, including but not being limited to acceptance tests of various substances or workpieces, evaluating jewelry and other noble metal products, investigating evidence collected from crime scenes, sorting on scrap yards and controlling industrial processes. Known methods of determining material composition can be roughly classified to chemical and physical processes, of which the latter typically mean exposing a part of the sample to excitation radiation and measuring the obtained response.
X-ray fluorescence (XRF) analysers are known that expose a sample to X-rays coming from a radiation source and collect the fluorescence radiation induced in the atoms and molecules of the sample. By analysing the relative intensity of fluorescent X-rays of different energies it is possible to deduce the relative proportions of various constituents in the sample.
Another known physical process for determining material composition is optical emission spectroscopy (OES), in which a portion of the sample material is heated to the state of plasma, so that the relaxation of excited states in the sample atoms and particles cause the emission of photons at energies that are specific to each atom and particle species. In a manner that is somewhat analogous to X-ray fluorescence analysis, a measured optical emission spectrum can reveal the relative amounts of certain constituents in the sample. In order to create the plasma various techniques can be used: for example an electric arc is ignited between a spark electrode and the surface of the sample, or a laser of high enough intensity is focused onto the surface of the sample. OES based on the last-mentioned technique is also known as LIBS (laser induced breakdown spectroscopy).
A U.S. Pat. No. 6,801,595 is known to disclose an analyser that combines both XRF and OES to a single apparatus. The analyser disclosed in said patent comprises an X-ray source and a fluorescent X-ray detector as well as means for performing optical analysis, preferably LIBS. A processor is arranged to collect the results of both the XRF and the OES measurements, so that both are available for determining the material composition of the sample. However, this apparatus has several drawbacks. The accuracy and reliability of the optical analysis made therewith is often poor, because it is difficult to obtain optical signals that would be high enough in intensity and representative enough of the overall composition of the sample.